Coenzyme M is a
coenzyme
A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that ass ...
required for methyl-transfer reactions in the
metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
of
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
l
methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are com ...
s, and in the metabolism of other substrates in
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
. It is also a necessary cofactor in the metabolic pathway of alkene-oxidizing bacteria. CoM helps eliminate the toxic epoxides formed from the oxidation of alkenes such as propylene.
The structure of this coenzyme was discovered by CD Taylor and RS Wolfe in 1974 while they were studying methanogenesis, the process by which carbon dioxide is transformed into methane in some anaerobic bacteria. The coenzyme is an
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
with the formula . It is named 2-mercaptoethanesulfonate and abbreviated HS–CoM. The
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
is unimportant, but the
sodium salt
Sodium salts are salts composed of a sodium cation and the conjugate base anion of some inorganic or organic acids. They can be formed by the neutralization of such acids with sodium hydroxide.
Categorization
Sodium salts can be categorized ...
is most available. Mercaptoethanesulfonate contains both a
thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
, which is the main site of reactivity, and a
sulfonate
In organosulfur chemistry, a sulfonate is a salt or ester of a sulfonic acid. It contains the functional group , where R is an organic group. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-o ...
group, which confers solubility in aqueous media.
Biochemical role
Methanogenesis
The coenzyme is the C1 donor in
methanogenesis
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group ...
. It is converted to methyl-coenzyme M thioether, the
thioether
In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A su ...
CH3SCH2CH2SO−3, in the penultimate step to
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
formation.
Methyl-coenzyme M reacts with
coenzyme B
Coenzyme B is a coenzyme required for redox reactions in methanogens. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate. The molecule contains a thiol, which is its principal site of reaction.
Coenzyme B reacts with 2 ...
, 7-thioheptanoylthreoninephosphate, to give a heterodisulfide, releasing methane:
: CH
3–S–CoM + HS–CoB → CH
4 + CoB–S–S–CoM
This induction is catalyzed by the
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
methyl-coenzyme M reductase
In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme tha ...
, which restricts
cofactor F430
F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR).
MCR catalyzes the reaction that releases methane in the final step of methanogenesis:
: + HS–CoB → + CoB–S–S–CoM
It is found ...
as the
prosthetic group
A prosthetic group is the non-amino acid component that is part of the structure of the heteroproteins or conjugated proteins, being tightly linked to the apoprotein.
Not to be confused with the cofactor that binds to the enzyme apoenzyme (eith ...
.
Alkene metabolism
Coenzyme M is also used to make acetoacetate from CO
2 and propylene or ethylene in aerobic bacteria. Specifically, in bacteria that oxidize alkenes into epoxides. After the propylene (or other alkene) undergoes epoxidation and becomes epoxypropane it becomes electrophilic and toxic. These epoxides react with DNA and proteins, affecting cell function. Alkene-oxidizing bacteria like ''
Xanthobacter autotrophicus
''Xanthobacter autotrophicus'' is a Gram-negative, aerobic, pleomorphic and nitrogen-fixing bacteria from the family of Xanthobacteraceae which has been isolated from black pool sludge in Germany.Deutsche Sammlung von Mikroorganismen und Zellku ...
''
use a metabolic pathway in which CoM is conjugated with an aliphatic epoxide. This step creates a nucleophilic compound which can react with CO
2. The eventual carboxylation produces acetoacetate, breaking down the propylene.
See also
*
Mesna
Mesna, sold under the brand name Mesnex among others, is a medication used in those taking cyclophosphamide or ifosfamide to decrease the risk of bleeding from the bladder. It is used either by mouth or injection into a vein.
Common side effec ...
– a cancer chemotherapy adjuvant with the same structure
References
Coenzymes
Thiols
Sulfonates
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